1. Field of the Invention
The present invention relates to a semiconductor device having a chip-on-chip structure, and to a semiconductor chip for use in such a semiconductor device.
2. Description of the Prior Art
Conventionally, semiconductor devices having so-called chip-on-chip structures have been proposed that are built by bonding a semiconductor chip to the surface of another semiconductor chip. A typical example is an LSI chip, constituting a gate array, having another LSI chip, constituting a memory, analog-to-digital conversion device (hereafter referred to as an A/D conversion device), or CPU, superposed and thereby mounted thereon.
However, in a semiconductor device having a chip-on-chip structure, it is necessary to design a pair of semiconductor chips that are to be bonded together to have pads in corresponding positions. For this reason, to upgrade an existing system, for example by increasing the capacity of a memory, by increasing the number of conversion bits of an A/D conversion device, or by increasing the number of processing bits of a CPU, it is necessary to renew not only the design of the LSI chip constituting such a device, but also the design of the gate array LSI chip to which it is bonded. That is, there is no choice but to develop and produce a completely new product.
This means that, every time a system is upgraded, a large amount of human energy needs to be expended on system upgrading including the modification of the manufacturing line.